The invention is situated in the field of packaging technology and concerns a method and a device in accordance with the generic terms of the corresponding independent claims. Method and device serve for the strapping of stacks of printed products. They are suitable in particular for being utilised with stacks of varying stack heights and for stacks of printed products with an edge, in the zone of which the product is thicker than in other zones, which reduces the stability of the stack as a result of its increased thickness. Printed products of this type are, e.g., folded newspapers or magazines with a bonded or stapled rear edge.
Printed products are laid out as an imbricated stream when coming from the rotary printing press or from a coil, but also from various other further processing devices (e.g., insert drums). For transportation and distribution, these printed products as a rule are stacked (in most cases in crossed stacks) and when so required the stacks are equipped with cover sheets and if necessary enveloped/wrapped and then strapped, so that they can be transported in a stable condition.
Devices for the strapping of stacks of printed products are known to the specialist, e.g., from the publication DE-3248788. These devices usually comprise a loop-shaped tape channel, means for the positioning of a strapping tape from a supply roll in the tape channel, means for the tightening and tensioning of the tape loop laid out in the tape channel around a stack positioned in the zone of the tape channel and means for locking the strapping around the stack and for cutting off the strapping tape locked around the stack from the supply roll. The tape channel is arranged and designed in such a manner, that it does not impair the feeding-in and the removal of the stack and in such a manner, that the strapping tape during tightening can be pulled out of the channel along its whole length without any problem.
The affixing of a strapping around a stack of printed products can be problematical, if the stack has not much stability and therefore is difficult to manipulate and has to be transported from a stacking shaft into a strapping position for the strapping operation, which is usually the case in known arrangements. In doing so, the stack has to be braked, strapped and accelerated again. Because the stack is relatively unstable, no great accelerations are possible, as a result of which the cycle time becomes relatively long.
In the publication WO-00/34127 a device is described, with which the problems mentioned above, which are caused by the instability of stacks, can be solved, in that the stacks are pushed out of the stacking shaft and immediately between two presser arms and are only released from the presser arms, when they have been enveloped/wrapped and as a result are stabilised at least to a limited extent. In doing so, the envelope is applied around the presser arms and the stacks are slid off the presser arms together with their envelopes/wrappings. Obviously an envelope of this type only leads to a stabilisation of the stack, if the enveloping material also after the withdrawing of the presser arms is still sufficiently tightly wrapped around the stack. This has the prerequisite, that the enveloping material is sufficiently elastic and can be sufficiently tensioned and/or that the stacked objects are sufficiently elastically compressible and can be pressed together sufficiently. If this is not the case, then the stack either before or after being enveloped has to be strapped in a separate operating step, whereby the same problems occur as are described above for either notxe2x80x94or insufficiently stabilised stacks.
The envelopment/wrapping in accordance with the publication mentioned above is implemented by moving the stack held pressed together by the presser arms against a curtain of enveloping material extending across its direction of conveyance, which curtain during the onward conveyance is placed around the preceding side of the stack and of the presser arms and on the trailing side of the stack can be closed to form a closed-in-itself envelope/wrapping. The enveloping material is simultaneously cut in such a manner, that it once again forms a curtin for a following stack.
It now is the objective of the invention to create a method and a device for the strapping of stacks of printed products, by means of which in particular relatively unstable and if so required already enveloped stacks can be strapped in a simple manner. The method and the device are to make as few as possible demands of the stack and of the strapping tape and in addition are to be adaptable without any problems for the strapping of stacks with differing stack heights.
This objective is achieved by the method and by the device as they are defined in the claims.
The invention in essence is based on the fact, that the stack held pressed between two presser arms is conducted to a strapping position in such a manner, as it is essentially described in the publication WO-00/34127 already mentioned above. The stacks are completely strapped with a strapping tape while the stack is held pressed together by the presser arms. In order, however, that the strapping is not subject to the same limiting conditions as the envelopment/wrapping in accordance with the publication mentioned, while the tape loop necessary for the strapping in the zone of the face sides of the stack is applied around the presser arms, whereby, however, in each of the two presser arms respectively a slot-like aperture is provided, to which the tape loop is aligned and through which the strapping tape is pulled during the tightening of the loop, in order for it to be able to be positioned directly on the stack also on the face sides of the stack.
The slot-like apertures of the two presser arms are aligned to one another and have two closed ends or a closed and an open end. They are designed in such a manner, that the closed ends rise above a stack held between the presser arms in such a way, that the strapping tape for the application of the tape loop can be led through the apertures from the zone between the presser arms next to the stack onto the outside of the presser arms and back again.
For the establishment of the tape loop, tape guides (e.g., a tape channel) have to be provided, of the type already known from known strapping devices. In this, a part of the tape guides is advantageously mounted on the presser arms and is conducted to the strapping position together with the stack held by the presser arms, where it complements stationary tape guiding parts.
Advantageously the strapping is only affixed, when an enveloping material has already been applied around the stack and the presser arms in such a manner, that the strapping is located outside the envelope. This means, that the envelope only has to fulfil a protection function, while the stack stabilising function is taken over by the strapping. In other words, this signifies, that the stack envelope is completely relieved of the conditions mentioned above regarding the elasticity of the enveloping material and/or concerning the compressibility of the stack. For the strapping no such conditions are applicable, because it is not affixed around the presser arms.
The two presser arms receiving a stack and compressing it, for example, have proximal and distal ends aligned to one another, are coupled to a drive with their proximal ends and in the manner of forks comprise at least one slot-shaped opening between two prongs extending towards the distal end and open at the distal end. The tape loop to be applied leads through the forks at the closed ends of the slot-shaped apertures, through the slot-shaped apertures over the outsides of the forks and is closed over the distal ends of the fork. The means for tightening/tensioning, for locking (e.g., welding together) and for cutting off the strapping tape are, for example, located outside one of the forks, whereby if so required to carry out its function it is temporarily moved closer to the stack through the slot-shaped aperture of the fork. The means mentioned, however, can also be located in an area between the two distal ends of the fork.
A stack of printed products is therefore positioned between two forks of a pair of forks assigned to one another, pressed together between them and in the pressed condition conducted to a strapping position for the strapping operation. In an enveloping/wrapping position preceding the strapping position or else in the strapping position itself, additionally a wrapping of the stack can be carried out.
For a multiple strapping operation, forks with more than two prongs and correspondingly multiple tape guides have to be provided.